Ferroelectric Tuning of Photocatalytic Water Splitting on Epitaxially-Strained TiO$_2$/SrTiO$_3$ Hetero-Structure

Using first-principles density functional theory (DFT) calculations, we show that the electric-dipole moment and epitaxial strain in heterostructures of TiO$_2$ with polar oxides such as SrTiO$_3$ can be used as control parameters to tune the activity of TiO$_2$ toward water splitting. Specifically, we find that the ferroelectric dipole of strained SrTiO$_3$ rigidly shifts the band-edge-energy positions of epitaxial TiO$_2$ films and affects the adsorption of relevant species (OH, H) on the TiO$_2$ surface. By varying the magnitude of the electric dipole moment and epitaxial strain, this effect can facilitate the oxygen evolution reaction and hydrogen production on TiO$_2$. In particular, our results show that a positive electric dipole pointed toward TiO$_2$ and compressive epitaxial strain can strongly reduce the barrier for oxygen evolution and thus significantly enhance the photocatalytic efficiency of TiO$_2$.